The GATE Grind

GATE 2018 CS – Question 24

Computer Networks · TCP: Flow Control, Congestion Control, Socket API · 1 mark · Multiple choice

Consider the following statements regarding the slow start phase of the TCP congestion control algorithm. Note that $cwnd$ stands for the TCP congestion window and MSS denotes the Maximum Segment Size.

(i) The $cwnd$ increases by 2 MSS on every successful acknowledgement.

(ii) The $cwnd$ approximately doubles on every successful acknowledgement.

(iii) The $cwnd$ increases by 1 MSS every round trip time.

(iv) The $cwnd$ approximately doubles every round trip time.

Which one of the following is correct?

  1. Only (ii) and (iii) are true
  2. Only (i) and (iii) are true
  3. Only (iv) is true
  4. Only (i) and (iv) are true

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Correct answer: (C) Only (iv) is true

Explanation

In slow start, $cwnd$ grows by 1 MSS per ACK, so it roughly doubles every round trip time. Only statement (iv) is true.